Search for: All records

The ammonia (NH3) and dimethyl ether (DME) mixture is a promising alternative fuel that offers the potential for cleaner combustion. This study presents an investigation of the autoignition-assisted flame speeds of stochiometric NH3/DME mixtures under conditions relevant to practical combustion systems. Experiments were conducted at pressures of 5 and 10 bar, gas temperatures ranging from 625 to 708 K, and three DME concentrations (10, 20, and 30%, mole fraction basis) in NH3/DME fuel mixtures using a rapid compression machine-flame (RCM-Flame) apparatus. For the majority of the autoignition experiments, first-stage ignition delay time was observed. Thus, the flame experiments were performed by igniting the spark both before and after the first-stage ignition delay time. The results are presented in terms of the Beta-Damköhler Number, defined as the ratio of spark ignition time to the first-stage ignition delay. The flame speed changes depending on the Beta-Damköhler Number, pressure, gas temperature, and DME concentration. The flame speed increases by increasing the temperature, decreasing the pressure, and increasing DME concentrations. However, the effect of Beta-Damköhler Number on flame speed is complicated: with 10% DME in the mixture, the flame speed is independent to Beta-Damköhler Number, and slight observed slight decrease of flame speed is due to the temperature drop during the post-compression period; with 20% DME in the mixture, at both pressures, the flame speed jumps after the first ignition delay (or Beta-Damköhler Number of one) , and remains constant before and after; similar behavior was observed with 30% DME in the mixture at 5 bar, however, at some temperatures, the flame speed increases at Beta-Damköhler Number of greater than one, and at 10 bar, the first ignition delay was short and flame speed was not measured at Beta-Damköhler Number of less than one. For all studied conditions, a linear trend was observed between burning velocity and stretch rate. Positive Markstein lengths were observed at most conditions, except for two specific gas temperatures (664 K at 5 bar and 671 K at 10 bar) with 30% DME, where negative Markstein lengths are found. One-dimensional laminar flame speed simulations agreed with measured data for Beta-Damköhler Numbers. less than one, but underpredicted the measured data at other conditions. 

The autoignition characteristics of ammonia (NH3) and dimethyl ether (DME) blends were examined in this research project. The study investigates the autoignition characteristics by measuring ignition delay times across a range of gas temperatures from 621 to 725 K and at pressures of 5, 10, and 20 bar by using a rapid compression machine (RCM). Ignition delays of NH3/DME blends, with DME concentrations in the fuel mixture ranging from 0 to 50%, were measured, simulated, and compared with JP-8 and JP-5 fuel ignition delays. At a pressure of 20 bar, blends containing 30 and 50% DME concentrations exhibited ignition delay times similar to those of JP-8 and JP-5. Furthermore, the fuel blend with a 30% DME concentration showed similar ignition delays at the lower pressures of 5 and 10 bar. Several kinetic models were used to model the autoignition and compared with the measured data. Simulation results fairly matched the measured ignition delays. Through rigorous experimental verification, this comprehensive analysis evaluated the reliability of existing chemical models and paved the way for further studies on customized fuel blends, thereby contributing to the ongoing debate on sustainable energy alternatives.